Proposals have been made in the past to provide an underground oil spill recovery system installed in one well using a first submersible pump to draw down the water table and create a "cone of depression" in the ground water. This "cone" funnels the oil floating on the ground water to the apex of the "cone" where it is recovered via a second submersible pump. The system includes a series of float switches to sense the relative levels of oil and water and to energize the appropriate pump. The system, however, requires a well having a 6 to 12 inch diameter casing. Such an oil recovery system is disclosed in U.S. Pat. No. 4,273,650.
Another underground oil spill recovery system is currently sold by Oil Recovery Systems of Greenville, N.H. The system, installed in one well, uses a submersible water pump to draw down the water table to create a "cone of depression" in the ground water table and thus allows oil to be drawn into the well. A floating oil recovery unit is then used to remove the oil from the well. The floating oil recovery unit uses a semi-permeable membrane which allows oil to pass but blocks the flow of water. Floats inside the unit electronically sense the presence of oil and actuate a pump located above and out of the well to remove the oil. This system requires a well casing having an inside diameter of approximately 24 inches. The system uses a single well to service an area encompassed by a circle having about a 100 foot radius and surrounding the well.
A proposal has been made for an oil detection system which signals the presence of oil residing on open waterways. The system includes a semi-permeable membrane which allows liquid hydrocarbons to pass while blocking the flow of water therethrough. Electronic sensors located inside the unit sense the presence of liquid hydrocarbons which have passed through the membrane. Such an oil detection and alarm unit is disclosed in U.S. Pat. No. 3,719,936.
None of the oil recovery systems described above discloses apparatus and a method for recovering liquid hydrocarbons from an underground site atop ground water without simultaneously removing the ground water itself in the process. The handling and disposal of the ground water removed to create the "cone of depression" is a major hindrance in the the use of the conventional recovery systems listed above. The problems incurred in the handling of such ground water are primarily due to costs since such systems require the following: Pumping equipment (a submersible water pump and water level control system with appropriate support systems, such as a power supply, structural supports, and a protective housing), ground water processing equipment (filters, valves, piping, storage tanks, and water purification equipment), ground water disposal procedures and equipment (injection wells or trenches and associated piping to deliver the water back into the ground), liquid hauling equipment to remove the ground water from the site if it cannot be put back into the ground, and fees associated with the use of disposal sites if the ground water is hauled away.
Another major problem arising from the use of the above systems is that the removal of ground water from an area will cause ground subsidence and will endanger buildings and other structures in the area. Further, the systems mentioned above use electronic sensors to monitor or sense the level and presence of oil. An electronic sensing unit in an oil recovery system increases the risk of fire and explosion.
None of the above systems are designed to function in small (2 to 4 inch) diameter wells which can be quickly and inexpensively installed. None of the above systems are designed to be used in a multitude of wells which are systematically drawn from in a prearranged sequence and controlled by a central, automatic control station. None of the above systems discloses a braking system designed to maintain the position of a hydrocarbon unit in a well casing regardless of the buoyancy of the recovery unit or the fluid levels. None of the above systems uses a track and lock mechanism inside a well casing to provide stability for the recovery unit and to hold the recovery unit in the desired location in the well casing.
Because of the foregoing drawbacks, a need has arisen for improvements in the recovery of liquid hydrocarbon residing on ground water due to spillage or other reasons.